Why, you ask? Well, he was giving the pop star the "ass-whooping that he deserves."
In the first clip released from Justin's Comedy Central roast, roast-master Kevin Hart warms up the audience and sets the tone for what's to come.
"Why invite me if you don't want it to get ugly? I don't understand that," Kevin says in the clip, in front of a crowd that includes a laughing Jaden Smith, Kendall Jenner and her sister Kourtney Kardashian.
But instead of going right in on Bieber, Kevin decided to crack some jokes on the panel of roasters. (Over the course of the night, Hart would go after the Biebs for everything from his brushes with the law to his relationship with Selena Gomez to his underwear modeling.)
"C'mon, we got the right dads to do it: we got Ludacris, we've got my man Snoop Dogg, Shaq," the "Ride Along" star cracks. "Usually, when I see this many brothers sitting together, Maury Povich is about to open an envelope. I've never seen anything like it."
And just think -- that's was just the warm-up. To see the full roast, which Justin called "one of the best nights ever," make sure to catch it when it airs Monday, March 30 at 10 p.m. ET/PT.